I. Field of the Invention
This invention relates to a method of grinding a monocrystalline sapphire wafer used with a semiconductor device.
II. Description of the Prior Art
A monocrystalline sapphire (hereinafter referred to as sapphire) has a hexagonal crystalline structure. A sapphire wafer used with a semiconductor device is fabricated in such a manner that the R plane {1102} of said wafer constitutes its surface. The surface or R plane {1102} of the sapphire wafer is conventionally ground by attaching the wafer to a wafer holder, linearly reciprocating the wafer holder, and contacting a rotating grindstone on the surface of the wafer. In this case, as shown in FIG. 1, the direction in which the wafer is held is defined by setting an orientation flat a (a plane defining an angle of 45.degree. with a projection of the C axis [0001] of the sapphire wafer c and intersecting the R plane at right angles) in parallel with the grinding direction b, or as shown in FIG. 2, setting said orientation flat a in a random direction relative to the grinding direction b. However, many of the sapphire wafers ground by the above-mentioned conventional process are considerably warped as a whole. The prominent warp (i.e., the overall deformation in surface height) of a sapphire wafer presents various difficulties in setting up a semiconductor device on said sapphire wafer, including, for example, the drawback that masking tends to be accompanied with displacement.